Process and system for removal of light ends and non-condensables to prevent buildup in an olefin/paraffin membrane separation process
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Solution Overview
Problem
The buildup of light ends such as hydrogen, methane, and ethane in propylene streams reduces the performance of column overhead compressors and membrane systems, failing to meet product specifications in existing purification processes.
Innovation Solution
A process involving a stripper column or a surge vessel is implemented to separate and remove hydrogen and lighter hydrocarbons from the propylene stream, utilizing a stripper column to produce a propylene-rich permeate stream and a propane-rich retentate stream, or using a surge vessel to separate the retentate into propane and lighter hydrocarbons, which are then routed to a gas concentration unit for further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a membrane unit is used to separate propylene and propane, then propylene concentration is improved, but light ends (hydrogen, methane, ethane) build up in the system reducing compressor and membrane performance
Solution Approach 1:
The patent extracts and removes light ends (hydrogen, methane, ethane) from the propylene stream using a stripper column positioned before the membrane unit. This prevents the accumulation of light ends that would otherwise reduce compressor and membrane performance, while maintaining high propylene concentration through the membrane separation process.
2Object-generated harmful factors
If a stripper column is added to remove light ends, then light ends removal efficiency is improved, but device complexity increases
Solution Approach 1:
The patent combines the stripper column with the existing C3 splitter and membrane unit into an integrated separation system. The stripper column integrates with the C3 splitter overhead stream, and the membrane unit processes the stripper bottom stream, creating a unified process flow that removes light ends while maintaining propylene/propane separation capabilities.
3Productivity
If the retentate stream is returned to the C3 splitter, then propylene recovery is improved, but light ends may accumulate in the recycle loop
Solution Approach 1:
The patent implements a feedback control mechanism where the retentate stream from the membrane unit is returned to the C3 splitter, and the stripper column continuously removes light ends from the C3 splitter overhead stream. This closed-loop system prevents light ends accumulation by continuously extracting them from the recycle loop while maintaining high propylene recovery through the membrane separation and recycle process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively removes up to 99% of ethane and hydrogen, preventing their buildup and maintaining compressor performance and product purity by ensuring efficient separation and routing of light ends, with the stripper column operating at specific pressures and temperatures, and the surge vessel providing a chilled outlet for light ends.
Implementation Method 1
sending said second top stream through a membrane unit to produce a permeate stream comprising a higher concentration of propylene than said second top stream and a retentate stream comprising a higher concentration in propane than said second top stream
Implementation Method 2
passing a gas stream comprising hydrogen and C1-C3 hydrocarbons to a stripper column to produce a stripper off gas stream from a top section of said stripping column and a bottom stream comprising C3 hydrocarbons
Implementation Method 3
sending said retentate stream to a surge vessel to separate said retentate stream into a propane stream and a surge vessel off gas stream comprising C1 to C2 hydrocarbons
Data Source
AI summary
Systems and processes are provided to prevent light ends such as methane, ethylene and ethane from building up in an olefin/paraffin separation system that uses a combination of a membrane and distillation column for this separation. In one embodiment a small stripper column is provided downstream from a selective hydrogenation reactor. In the other embodiment, a surge vessel with a receiver is added to the retentate stream of the membrane unit.